Weeks remained in the game for two more innings before the A's lifted him for pinch-hitter Cliff Pennington in the bottom of the fourth.
A's manager Bob Melvin said Weeks is day-to-day and probably won't play on Sunday, but Weeks said he's had this injury before and he thinks he'll be able to play.
"I've come back the next day before, and I"m looking forward to doing that this time," Weeks said.
Weeks, the A's switch-hitting second baseman, had been struggling with a .192 average coming into the game, but he had singled in his two at-bats on Saturday night. In his second trip, he stumbled just as he lined the ball into right field.
Weeks' injury came just hours after the A's had placed their cleanup hitter, Yoenis Cespedes, on the disabled list with a strained muscle in his left hand.
Jeff Fletcher is a contributor to MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.